Abstract

A well defined spectrum of peaks in d2I/dV2 vs V has been obtained with a tunnelingmicroscope immersed in liquid helium. The positions of the peaks correspond closely to the energies of the phonons of the graphite sample and the tungsten tip. We propose that electrons coupling to the bulk phonons near the tip to sample gap cause the observed increases in the tunneling conductance. Spectroscopic imaging at a phonon energy shows spatial variations of the vibrational spectra on an atomic scale.